Hello,
I'd just like to post my brief experience of the M8 camera so far, picked one up this afternoon, had the M7 for 12 months before hand. Both UK models.
With the M7 I had several issues:
1) Purple tints if bright light to the sides out of the picture
2) Focus would hunt in anything but bright light. It would go from out of focus, through in focus back to out of focus and then give up
3) White balance seemed to be calculated from the angle you were holding the phone and have little to do with the scene, could get all sorts of shades simply by tapping the same spot on the screen to make it refocus, almost trippy when the focus was hunting.
4) Struggled with a mix of bright and dark elements to a scene, you'd get blown out portions or black portions depending on where you focused, HDR seems pointless.
5) Very high compression, 4mp is low, but even still, the loss of detail is huge.
6) Noisy in low light, white balance defaults to 'red tint'
7) Flash assist focus is slow and cannot be turned off, having a flash in your face is bad enough, staring at it while the phone focuses is a no-no.
M8 vs M7:
1) None seen at all, it's dark outside but even inside with the bright main lights to one side of the frame there is no colour issue at all, huge improvement
2) Less than 300ms? In good light yes, certainly seems faster than the M7, but whilst I see less of the hunting in dim light, it is still there and just unforgivable when you're advertising a phone with a depth sensing camera. That said, whilst it does go through the entire focus range, it does then snap back, most of the time, to a reasonably good focus. It almost as if it falls back on the depth data if it can't focus optically. But the whole process makes its use as social snapper a bit limited I feel. I certainly wouldn't rely on it to catch any in the moment snaps inside with the lights off.
3) No issues whatsoever, seems to be perfect at all times, another huge improvement.
4) I don't see any improvement here at all, it's dreadful. Shame you can't decouple the exposure point from the focus point or have multi-point exposure.
5) I think this is actually worse
6) I think this is worse also, though I have not tried the max ISO feature
7) Same, though I noticed on several occasions it used the flash to focus but not capture. Can't turn the flash assist on or off separately to the flash for capture. Flash exposure does seem better though.
New issues (or at least ones I've not had on the M7):
1) Screen appears to 'flicker' if pointed at a cluster of bright lights and you move the phone around a bit, I'd suggest some auto-gain or exposure control doesn't have very fine control and is visibly jumping between one level and another.
2) Re-focusing only seems to work if the photo was in focus originally. One of my test shots in dim light was out of focus, I tried to refocus it and it made little difference. I did wonder whether this feature would compensate for the focusing problems...

3) No Zoe, despite updating it from the Play store...? This is a killer feature, all other issues aside.
The camera is better, no doubt about it, but better and good are not the same at all, and this is still a disappointing camera for low light unless you have a tripod and a static scene. Hopefully all resolvable with some software updates.